What’s an Adverse Drug Reaction?

We take a lot of pills! Researchers estimate that in any given week, 4 out of 5 adults will use prescription medicines, over-the-counter (OTC) drugs, or dietary supplements of some sort. Moreover, 66% of all US adults use prescription drugs. And nearly 1/3 of adults take 5 or more different medications. Although medications can make us better, taking multiple medications can make us sicker. Unfortunately, an adverse drug reaction can make you sick – sometimes sick enough to need hospitalization.

Unsurprisingly, the more medications you take, the greater the risk of a serious, potentially life-threatening drug interaction. Clearly, this is a scary scenario for all of us who rely on medications to keep us healthy.

Fortunately, you can take steps to reduce your risk of adverse drug reactions. Read on to learn how!

What is the definition of an adverse drug reaction (ADR)?

An adverse drug reaction (ADR) occurs when a patient has an unexpected or dangerous reaction to a medication. A patient may develop an ADR after a single dose of medication, after the prolonged use of a drug, or when there is a negative interaction between 2 or more medications.

More specifically, The American Society of Health-System Pharmacists (ASHP) defines an ADR as “any unexpected, unintended, undesired, or excessive response to a drug” that leads to any of the following:

• Requires stopping the drug.
• Requires a change in the drug therapy.
• Leads to a modification of dose (except for minor dosage adjustments).
• Necessitates admission to a hospital.
• Prolongs a stay in a healthcare facility.
• Requires supportive treatment.
• Significantly complicates diagnosis.
• Negatively impacts prognosis.
• Leads to temporary or permanent harm, disability, or death.

There are several other names for these incidents: adverse drug event (ADE), adverse effect and adverse event. To minimize confusion, this post will refer to these situations as adverse drug reactions, or ADRs.

What is the difference between an adverse drug reaction and a side effect? 

There are defined differences between side effects and ADRs. Pharmacy Times describes the difference between side effects and adverse events as follows:

An adverse event is an unexpected reaction that happens when a medication is taken correctly. Adverse reactions are often completely unpredictable, due to patient-specific susceptibility factors such as drug allergies and intolerances.

On the other hand, a side effect is a more predictable undesired effect from taking a medication. In fact, doctors usually warn patients about potential side effects.

How do adverse drug reactions occur?

ADRs occur for a number of reasons, including:

• When patients take too much of a medication. For example, when pharmacists or nurses make errors in dispensing medication. Or when patients take the wrong number of pills at home.
• When a medication is mixed with something it should not be mixed with, including an additional medication. For example, if your doctor doesn’t have a complete list of all your medications, he/she may prescribe a new medication that should not be used in conjunction with another medication you’re already taking.

What are the symptoms of an adverse drug reaction?

The patient’s health can suffer, and unfortunately, some patients die from ADRs.

There are many physical signs and symptoms of an ADR – far too many to list in this post. However, symptoms include the following: rashes, itching, bleeding, joint pain, heart problems, confusion, hallucinations, over-sedation, falls, difficulty breathing, dizziness, depression, and diarrhea.

What drugs cause adverse drug reactions?

Although many drugs can lead to ADRs, some medications carry a higher risk. For instance, 66% of hospitalizations in older patients due to adverse drug reactions are caused by 4 drugs or drug classes: warfarin, insulin, oral antiplatelet drugs, and oral hypoglycemic drugs.

Importantly, some medications require patients to get regular blood tests to make sure they are on the right dosage. Interestingly, these medications are more like to cause serious adverse drug reactions. In fact, studies show that over 40% of emergency room visits that end with patient hospitalizations are caused by a few medications that require blood test monitoring.

Senior patients experience more ADRs.

Unfortunately, seniors are more likely to experience an ADR. For instance, hospitalization rates due to adverse drug reactions are 4 times higher in patients over 65, as compared to adults under 65. In fact, research shows that although only 14% of the US population is over 65, they account for 56% of hospitalizations for adverse drug events.

Additionally, experts estimate that in a recent 10-year period, 35 million seniors (65+ years old) visited an emergency room for an adverse drug event. Furthermore, they estimate there were more than 2 million admissions during this time for serious adverse events.

Why so many ADRs among seniors?

Firstly, seniors take a lot of medications. For example, more than 40% of seniors take five or more prescription medications a day, which is an increase of 300 percent over the past two decades. Moreover, almost 20% take ten drugs or more. And that is for prescriptions only! If you include over-the-counter medications and supplements, 67% of seniors take 5+ medications daily. Importantly, as the number of medications rises, the risk of a serious, potentially life-threatening, drug interaction increases.

Additionally, seniors receive their medications from a wide range of medical providers, who generally do not speak to each other about patient cases. Furthermore, in most cases, there is no single medical provider responsible for keeping track of all medications and making sure no drugs could negatively interact. Therefore, it’s easy for a potential ADR to slip through the cracks.

And making matters worse, although seniors take a large portion of medications, few drugs are adequately tested in seniors.

As we age, our bodies change in important ways.

Importantly, there are significant differences between younger and older patients, often not realized by doctors or patients, including a variety of health reasons that make seniors more vulnerable to ADRs, as follows:

• Seniors generally weigh less and have different body composition than younger people, which impacts the concentration of medication in their bodies, and how long medications stay in their bodies.
• Seniors’ livers can’t process drugs as well as in younger people.
• Kidneys of seniors can’t clear drugs out of the body as well as in younger people.
• Seniors have increased sensitivities to many medications.
• Older adults can’t maintain their blood pressure as easily as younger people, making them more vulnerable to dizziness, falls, etc.
• Medications can make it even harder for seniors to modulate their temperatures, potentially causing life-threatening, or fatal, changes in body temperatures.
• Seniors are more likely to have at least 1 disease that alters their response to medications.

Special alert for dementia patients.

An analysis of Medicare claims found that almost 14% of people with dementia who lived outside nursing homes had overlapping prescriptions for 3 or more drugs that act on the central nervous system. The drugs of concern are antidepressants, antipsychotics, anti-epileptics, benzodiazepines, non-benzodiazepine receptor agonist hypnotics, and opioids.

Unfortunately, taking 3 or more drugs like these can increase the risk for impaired cognition, fall-related injury, and even death.

Read Medication Issues for Seniors to learn more.

Are ADRs preventable?

In many cases, ADRs can be prevented.

Researchers analyzed data from 24 studies and found that:

• Among non-hospitalized adults, 52% of adverse drug reactions were preventable.
• For hospitalized adults, 45% of adverse drug reactions were preventable.

Doctors and other medical professionals can reduce the risk of ADRs by making sure patients receive the right drug at the right dosage, while also ensuring each medication does not negatively interact with other medications and conditions. Clearly, that doesn’t always happen. So, what can you do to reduce your risk of an ADR? Read below to learn tips.

Worried about an adverse drug reaction? 

Certainly, you don’t want your medication to make you sicker. If you think you’re experiencing an ADR, tell your doctor your experience, including as many details as possible. For instance, what symptoms did you experience? How bad were the symptoms? When did the symptoms start? How long did it last?

Minimize you risk.

Importantly, consider these steps to minimize your risk of an ADR:

• Make sure each doctor knows ALL the medications you are taking, including over the counter medications and herbal supplements.
• Ask your doctor or pharmacist if any of your medications require blood testing. If so, stick with the blood testing schedule and pay extra attention to make sure you take these medications as prescribed.
• Check your medications on WorstPills.org to see if you take medications considered risky. Discuss any findings with your doctor. Importantly, do not stop taking medications without talking to your doctor.
• Always carry your list of medications with you. You can keep a piece of paper in your wallet, make a note on your cell phone, or use any of the medication apps available (see our Resource page for reviews of medication apps).
• Use the same pharmacy for all your medications, so they can check for possible ADRs. And you can ask your pharmacist to review your list of medications, including over-the-counter and supplements, to identify possible issues.
• At least once a year, bring a complete list of all medications, including over-the-counter drugs, to your primary care doctor for review. Importantly, ask if any of the medications can negatively interact. Furthermore, ask if any medications can be eliminated, or if any dosages can be reduced.
• Make sure you properly understand when and how to take each medication.
• Since it’s easy to make mistakes, set up a system to organize your medications.
• Use an alarm system, on your cell phone, watch, or other timer to help you remember to take each medication on time.
• For complicated medication regimens, keep track with the ZaggoCare Daily Medication Chart (scroll down to the footer for a link to our downloadable chart).

Special concerns for seniors.

• If you, or your loved one, is over 65, you can check the American Geriatric Society’s Beers Criteria list of medications deemed potentially dangerous for seniors. Again, discuss your findings with your doctor.
• If your loved one has dementia, talk to his/her doctor about reducing central nervous system drugs if he/she takes 3 or more from the list above.

Learn more…

For more tips on reducing your risk of medication-related issues, read these posts:

• Reduce Your Risk of Medication Errors.
• Dangers of Black-Market Medications – More Common Than you Think.
• Tips to Take Medication as Prescribed.
• Are Antibiotics Helpful or Harmful? What You Need to Know.
• Doctors Prescribe Too Many Medications.
• Are Medications Safe?
• Is Off-Label Medication Safe?

NOTE: I updated this post on 6-4-23.